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Monday, June 6, 2016

A few
weeks ago, as I’m sure most people reading this blog know, Elon Musk, the CEO
of SpaceX announced plans to land their Dragon spacecraft, largely at the
company’s expense, on Mars.While this
plan is audacious enough, Musk has previously positioned SpaceX’s Dragon
capsule as an all-purpose lander suitable to explore almost the entire solar
system.

Since
Musk’s announcement, I’ve been doing research and thinking about what the
availability of a commercial planetary lander might mean for planetary exploration.Even if landing the company’s Dragon
spacecraft on Mars proves to be a one-time event, it will demonstrate that the
technologies for planetary missions have become widely available.

What if,
though, SpaceX’s Dragon spacecraft becomes a standard catalog item that could
ordered, the way a launch vehicle is?What might the impact be on planetary exploration?As I thought about this, I concluded that
three questions are key: How flexible will the Dragon spacecraft be as a
payload delivery vehicle?How far afield
can it operate in the solar system without design changes so massive that it
becomes necessary to essentially redesign it?And how will be missions it might fly be paid for?

Mock up of the Dragon version 2 capsule for Earth orbital missions. Credit SpaceX.

First,
some background on the Dragon spacecraft.SpaceX currently is using the first version of the uncrewed Dragon
spacecraft to deliver supplies to the International Space Station.It is also being being funded by NASA to
design a crewed version of the spacecraft to deliver astronauts. (I couldn’t
find out what proportion of the Dragon development is being funded by NASA
versus by SpaceX’s own funds.)Musk has
ensured that this second version incorporates key technologies such as heat
shields that can survive atmospheric entry from interplanetary speeds and built
in thrusters that allow soft landings.(Phil Plait at Slate
magazine
has an excellent article on the technologies involved.Wikipedia has additional information.)

Designing
a craft for interplanetary flight requires numerous differences from a craft
designed to operate in low Earth orbit for short periods of time and then return
to our world.Systems must be able to
function for months to years.Electronics must be able to function in the harsher radiation
environment outside the Earth’s magnetosphere.The communications system must be able to transmit and receive data over
distances of hundreds of millions of kilometers.There will be hours to days between
communications periods, requiring the craft to be able to operate autonomously.

Artist's conception of the Red Dragon capsule on the surface of Mars. Credit: SpaceX.

To
operate as a long-lived lander on the surface of a planet, the spacecraft must
deploy solar panels to generate power after touch down.(I’ve not heard of any plans to use
plutonium-based power generators for the Dragon spacecraft.)Batteries must be carried and recharged to
keep the spacecraft operating during the night.And especially on frigid Mars, the spacecraft will need insulation and
heaters to keep it warm.

These
problems are well known, and we can presume that SpaceX’s engineers have
designed the Dragon spacecraft and their subsystems with these issues in
mind.It’s worth pausing for a moment to
consider the kind of commitment this implies to SpaceX’s commitment to
revolutionize Martian exploration because these enhancements likely aren’t
cheap.

By making
these investments in the basic Dragon spacecraft design, referred to as the Red
Dragon for Mars missions, SpaceX can take advantage of what is likely to be a
low volume assembly line building these craft.While NASA has designs of its own it can reuse to land on Mars, flights
are likely to be infrequent enough that their components may gradually become
obsolete and the expertise to rebuild and test them may fade.SpaceX presumably will be building several
Dragon spacecraft a decade, allowing it to gradually update the design and keep
its expertise intact.The result will likely
be a lander that may be substantially cheaper than NASA reusing its existing
designs for some Mars missions.

How
Flexible is the Interplanetary Dragon Lander?

I know of
two proposals for scientific missions that would use the Red Dragon spacecraft.
One, IceBreaker, led by NASA’s Chris
McKay would return to the northern polar plains of Mars to further investigate
the subsurface ices found there for habitability and signs of life.The appeal of the Dragon spacecraft appears
to have been its expected low cost.McKay has also proposed the IceBreaker mission using a near copy of the
much smaller NASA Phoenix and InSight landers.The instruments would have weighed a few tens of kilograms, barely
taking advantage of the payload that the Red Dragon could deliver.The Dragon lander (dubbed the IceDragon for
this concept), however, could have carried a much larger drill than the
Phoenix-derived lander, allowing samples to be collected from much further
below the surface.(The one published
abstract for the IceDragon mission from several years ago proposed a 2 meter
drill.Technology development since then
might allow much deeper
drilling.)

Conceptual design for the IceDragon version of the Red Dragon capsule that could be sent to sample the icy plains of Mars' arctic regions. Human figure shown for scale. Credit: NASA.

The
second proposal would be to use the Dragon spacecraft to deliver a launch
vehicle to return samples directly from the surface of Mars to the Earth.This concept takes full advantage of the
payload mass and volume offered by the Dragon.Other concepts proposed to return samples to Earth envision two
missions.The first would land on Mars
and launch a sample canister into Martian orbit.The second would retrieve the canister and
perform the voyage to Earth.The large
ascent vehicle enabled by the Dragon would, the proposers argue, combine these
two functions to lower costs, complexity, and risk.

Unfortunately,
this proposal requires that a rover already be on Mars that could deliver a
canister with samples to the Dragon spacecraft.While NASA’s planned 2020 Mars rover will collect samples, it will leave
them on the surface for a later rover to collect and return to an ascent
vehicle.There isn’t the payload mass
for the proposed Dragon mission to carry its own fetch rover and a direct-to-Earth
ascent return vehicle, although it could launch samples into Martian orbit if
it has to carry its own fetch rover according to the proposers.

Conceptual design for the Red Dragon used to carry a Mars Ascent Vehicle (MAV) and an Earth Return Vehicle (ERV). Credit: NASA.

There’s
much we don’t know about the Red Dragon design.Will it be suited only to missions where the scientific investigations
are limited to the immediate landing site where robotic arms could reach such
as these two proposals?That would
suggest missions to locations where homogenous conditions exist over large
areas such as the polar plains of Mars.

A
variation of the proposal to use the Dragon design to return samples from Mars
would be to use it to return samples from different regions of the moon or from
some of the larger asteroids.Since the
scientists proposing lunar sample returns are interested in broad regional
differences in composition, grabbing samples with an arm in the immediate
vicinity of the lander would meet their goals.

However,
many of the goals for lunar and Martian exploration require rovers that can
reach and study or sample multiple locations across within a much larger study
area.I have not seen any analysis about
whether delivering a capable rover would be a feasible extension of the Red
Dragon’s design.Could the Dragon design
host a moderately large rover (smaller than the Curiosity rover but perhaps
bigger than the Opportunity rover) and deploy it to the surface by including a
large hatch and a ramp or crane?

NASA
already has two current, proven designs for Martian landers.The first, used for the Phoenix and InSight
missions, delivers a few tens of kilograms of instruments using a small,
stationary lander.The key advantage of
this platform is that it provides a soft landing, and its low stature provides
easy access to the surface.The second
system used parachutes and a rocket-powered skycrane to deliver the Curiosity
rover to the surface (and the design will be reused for the 2020 rover).It also places up to 930 kilograms of rover
directly on the surface, eliminating the need for ramps to get the rover off
the lander.The landing system is also
designed with the myriad of safety requirements needed for a rover/lander to
use a plutonium power supply.

The Red
Dragon will be able to deliver a slightly more massive payload, about 1000
kilograms.While the payload space
appears large by the standards of most planetary landers, it doesn’t appear
large enough to carry a duplicate of the Curiosity rover.Unlike the skycrane landing system, the
payload will sit inside a large spacecraft, well above the ground.Long robotic arms or drills would be needed
to bring surface samples to instruments inside the spacecraft or place small
instruments on the surface.Delivering a
large package such as a rover to the surface would require ramps or a
crane.I expect that these problems are
solvable, but they create a level of complexity that NASA’s skycrane system was
invented to avoid.

Comparison of the sizes of the Dragon capsule (left) and the Curiosity rover entry and descent system. The Dragon capsule would not have the width to carry a Curiosity-sized rover, but likely could carry a smaller rover to the Martian surface. Credit: NASA.

Beyond the
Moon and Mars

Musk has been quoted saying that the Dragon capsule can be used to
explore almost any world in the solar system: “With Dragon launched on a Falcon
Heavy, it can go pretty much anywhere in the solar system, because that’s a
heck of a big rocket…Dragon 2 is
capable of transporting scientific payloads to anywhere in the solar system,
with a liquid or solid surface, with or without an atmosphere. So Dragon is
really a crew transport and science delivery platform…Dragon, with the heat shield, parachutes and
propulsive landing capability, is able to land on a planet that has higher
entry heating, like Mars. It can also land on the Moon, or potentially conduct
a Europa mission.”

Musk’s claim appears to touch
on three separate issues.The first is
whether the Falcon Heavy could propel a Dragon spacecraft to any location in
the solar system.The answer likely is
yes.For our moon, Mars, and Venus, the
launcher will be able to send the Dragon directly to these worlds.If the Falcon Heavy cannot send a Dragon
directly to Mercury or the outer planets, it certainly could launch it on a
trajectory that would use Venus and/or Earth gravity assists to provide the
additional velocity needed.

The second issue is whether the
Dragon could land on these more distant worlds, which breaks into two
parts.The first is how the Dragon
capsule would kill the high approach velocity when it reaches its
destination.The atmospheres of Mars,
Venus, and Titan can kill much of the speed.It’s less clear to me whether the Dragon spacecraft would carry enough
fuel to first brake into, say, Jovian orbit and then kill the remaining
velocity to land on Europa.(A direct
landing on Europa without entering Jovian orbit also would need to kill a lot
of speed.)Musk’s statements suggest it
could, but for now we lack details.

The third issue is whether the
Dragon spacecraft could deal with the special environmental issues at various
worlds.The moon and Mars are reasonably
straightforward challenges both because of their proximity and their
comparatively (for planetary destinations) benign environments. By contrast, while
the Mercurian poles are cool, the spacecraft would need to deal with intense
solar heating on the way to this world.The surface of Venus is intensely hot and has a crushing atmospheric surface
pressure.Jupiter’s moon Europa sits
deep within an intense, electronics frying, radiation belt.Titan’s surface is as bitterly cold as Venus’
is broiling.Landing on a small asteroid
or comet may require special adaptations such as harpoons to hold the capsule
on the surface.Traveling to any world
beyond Jupiter will require a radioisotope generator for power (Saturn might be an exception).It is possible to design
spacecraft to handle any of these challenges.Missions have been proposed to land on each of these worlds, but using
custom designs that take into account the unique challenges of each
environments.Would it be cost effective
to modify the Dragon spacecraft to handle the challenges of any of these
worlds, or more cost effective to design a custom spacecraft?

There’s also the question of
whether a prior scouting mission would be needed.For the moon and for high priority locations
on Mars, existing high resolution images would allow mission planners to
identify precise locations of safe terrain within otherwise rugged but
scientifically interesting terrains.The
same will be true for selected sites on Europa following NASA’s planned Europa
Multiple Flyby mission.What about a
world with only coarse resolution mapping or none at all?

Example of the rugged terrain the salt deposits of Ceres are found on. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA.

As a thought experiment, I
considered a Dragon mission to land on the asteroid Ceres to explore the salts
on the surface that have erupted from a likely (now frozen?) subterranean
ocean.We have moderate resolution (35
meters) images of the surface from the Dawn spacecraft currently orbiting that
world.The images of the terrain where
the exposed salts are found that I’ve seen, however, appear quite rugged at 35
m resolution.And a lot of
lander-killing ruggedness can hide within that scale of resolution.For assessing a potential Martian landing
site, by comparison, NASA likes to have images with sub-meter resolution.I’m sure that the Dragon capsule
or its service module could physically carry a high resolution camera to scout
for safe landing sites.But would the
spacecraft have the precise pointing capability to accurately aim the camera and
the stability to prevent image jitter?Again, solutions to these problems are well known, but is this something
that would have to be added to the Dragon spacecraft?

Who Will Pay for Interplanetary
Dragon Missions?

Until we
know more about the capabilities of the Red Dragon capsule, it is hard to know
what its advantages and disadvantages will be compared to existing lander
designs.It may provide a significant cost
advantage – remember that likely assembly line of Dragon spacecraft.However, the lander hardware is just one part
of the cost of a mission.There is still
the cost of the launch, the instruments, potentially a rover or a launch
vehicle for sample return, and operations.

Even if
the cost of a Red Dragon landing were free, these other costs would drive the
total mission costs to several hundred millions of dollars.This puts a Red Dragon-based mission in
competition for funding with all the other missions planetary scientists would
like to conduct.A lunar or Martian
landing mission may be selected by NASA only once a decade, and the Red Dragon
may or may not be the most suitable design.

As an
alternative, perhaps SpaceX will schedule a Martian landing every two years or
so and will sell payload space to space agencies, universities, and even
private companies to cover costs.Then
the cost to any individual space agency, university research group, or company
might be relatively small – a few million or tens of millions of dollars.

Or Musk
may use the profits from SpaceX or a portion of his personal fortune to drive
his own program of Mars robotic exploration.From his statements we know he wants to eventually take humans to Mars.Perhaps Red Dragon is a stepping stone to
that grander vision.

Red
Dragon is possible because of the vision and drive of its founder, Elon
Musk.He made a strategic decision to
build a capsule that could land on Mars as well as meet NASA’s needs in near
Earth orbit.We will need to wait to
learn what types of landed missions that vision will encompass and which worlds
beyond Mars Musk wants to explore.

About Me

You can contact me at futureplanets1@gmail.com with any questions or comments.
I have followed planetary exploration since I opened my newspaper in 1976 and saw the first photo from the surface of Mars. The challenges of conceiving and designing planetary missions has always fascinated me. I don't have any formal tie to NASA or planetary exploration (although I use data from NASA's Earth science missions in my professional work as an ecologist).
Corrections and additions always welcome.